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arm64: module: don't BUG when exceeding preallocated PLT count 

When PLTs are emitted at relocation time, we really should not exceed
the number that we counted when parsing the relocation tables, and so
currently, we BUG() on this condition. However, even though this is a
clear bug in this particular piece of code, we can easily recover by
failing to load the module.

So instead, return 0 from module_emit_plt_entry() if this condition
occurs, which is not a valid kernel address, and can hence serve as
a flag value that makes the relocation routine bail out.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel 2018-03-06 17:15:31 +00:00 committed by Will Deacon
parent e03e61c317
commit 5e8307b9c6
2 changed files with 4 additions and 1 deletions
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3
arch/arm64/kernel/module-plts.c
View File

@ -36,7 +36,8 @@ u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela,
return (u64)&plt[i - 1];
pltsec->plt_num_entries++;
BUG_ON(pltsec->plt_num_entries > pltsec->plt_max_entries);
if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
return 0;
return (u64)&plt[i];
}

2
arch/arm64/kernel/module.c
View File

@ -386,6 +386,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
ovf == -ERANGE) {
val = module_emit_plt_entry(me, loc, &rel[i], sym);
if (!val)
return -ENOEXEC;
ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2,
26, AARCH64_INSN_IMM_26);
}